The invention relates to a sine-cosine modulator comprising at least two comparators, two integrators, a power switching stage, an LC low-pass filter, and a low-frequency signal input or control-voltage input and a low-frequency signal output or DC voltage output.
Analog power amplifiers for low-frequency AC voltages in the audio-frequency range or voltage stabilizers are replaced in a number of applications in the prior art with pulse-width modulation amplifiers or switched-mode voltage converters that have a significantly higher level of thermal efficiency vis-a-vis the analog circuits. Self-oscillating pulse-width modulation amplifiers have better signal-processing or sound quality than clocked pulse-width modulation amplifiers that are driven by an external oscillator.
A self-oscillating pulse-width modulation amplifier of this type that not only has a significantly higher level of thermal efficiency vis-a-vis analog power amplifiers, but also better sound quality, is described in DE 198 38 765 A1 (“Selbstschwingender Digitalverstärker” [“Self-Oscillating Digital Feedback Amplifier”]). A drawback is that the natural frequency f is dependent upon the modulation factor with the relationship f=f0*(1−M2). The modulation factor or excitation factor is consequently limited to approx. 60% in practice.